Should the US have entered WW2 Earlier?

[The Mikado]

No, though an earlier embargo (1936 for Italy, 1937 for Japan, and 1938 for Germany), more vigorous rearming, and increased willingness to accept refugees would have been good. Perhaps a proto-Lend-Lease for China starting in 1937.

[The Mikado]

Yes, of course (cares about human lives)

What possible justification would we have had? We were not part of the Anglo-French ultimatum to defend Poland, we were not allied with Britain, France, or Poland, nor were we allied with the Republic of China, despite our very warm relations with Britain, France, and China. The United States had an armed force in 1939 rivaling titans like Spain, and it would take two years of buildup between 1939 and 1941 before we were even on paper a serious military force again. Outside of economic pressure like the earlier embargoes I advocated, what position would we have been in to do anything whatsoever on the European front without over a year's worth of preparation?

The Pacific theater is a different beast due to the US Navy's still-considerable power, but then again, war with Japan not involving war with Germany and Italy is not exactly what this question is about. I could actually see that as a more plausible option, especially given America's massive financial and humanitarian and personal interests in China in the 1930s and Japan's naked coveting of the Philippines.

EDIT: War between the United States and Japan over dominance of the Pacific Rim was coming, coupled with WWII or not.

[The Mikado]

Yes, of course (cares about human lives)

What possible justification would we have had? We were not part of the Anglo-French ultimatum to defend Poland, we were not allied with Britain, France, or Poland, nor were we allied with the Republic of China, despite our very warm relations with Britain, France, and China. The United States had an armed force in 1939 rivaling titans like Spain, and it would take two years of buildup between 1939 and 1941 before we were even on paper a serious military force again. Outside of economic pressure like the earlier embargoes I advocated, what position would we have been in to do anything whatsoever on the European front without over a year's worth of preparation?

The Pacific theater is a different beast due to the US Navy's still-considerable power, but then again, war with Japan not involving war with Germany and Italy is not exactly what this question is about. I could actually see that as a more plausible option, especially given America's massive financial and humanitarian and personal interests in China in the 1930s and Japan's naked coveting of the Philippines.

EDIT: War between the United States and Japan over dominance of the Pacific Rim was coming, coupled with WWII or not.

Well, obviously the US was in an isolationist mood back then and we didn't have formal treaty obligations, so to a certain extent this is 20/20 hindsight, but uh... what justification?  Defending the oppressed Poles is justification enough, to say nothing of the other atrocities and genocides that would come to light later (and, if we were better, more observant people back then, would have probably been able to bring to light).  Do they not count as victims to you?

I'm not saying that we necessarily could have jumped in immediately.  If we needed some months to ramp-up, then okay, fine.  We should have been in by the Battle of Britain, though.

Defending the Poles would take us into war, all right, but war with the USSR as well, and the Katyn massacre of tens of thousands of Polish political, economic, and societal luminaries is as egregious as anything the Germans were doing in the fall of 1939/spring of 1940.

From the perspective of defending beleaguered small states from aggression, what separates the German 1939 assault on Poland from the Soviet 1939 assault on Poland?

Edit: in general, war for humanitarian reasons/"responsibility to protect" isn't an international relations concept I'm comfortable with.

Edit 2: Let's make this easier. What sort of morality would dictate that the United States has a moral obligation to protect Poland from Greman aggression, but does not hold a moral obligation to protect Poland from simultaneous Soviet aggression? I've been flipping your post around in my head all morning and I'm puzzled, I really don't get what kind of moral code would say that one was a moral obligation to assist and the other was not.

[The Mikado]

The language of moral obligation is tricky. It implies Kant's doctrines that if you are obligated to do something, you have to do it every time. That's my issue with obligation to protect:it's an open-ended misdion to perpetual war. Where does aggression stop? Is North Vietnam invading South Vietnam an act of aggression that must be defended against? The PRC's invasion of Tibet? The iraqi incasion of Iran? Congo's neighbors' invasions of it in the 1990s? An obligation to protect countries against aggression is an insane open-ended route to endless war.

Protecting countries not allied with us is not and should not be a controlling interest in the American decision to go to war.

That's not to say that, as stated before, the US did all it could. Earlier embargos (as said before, 1936 for Italy, 1937 for Japan, and 1938 for Germany), a Lend-Lease for China in 1937 and France and Britain in 1939, and a commencement of rearmament in 1937 rather than 1940 would be beneficial, along with more open refugee policies and increased aid to the Red Cross.